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    Cam Shafts

    I know i have been bothering a bunch of you over the past 2 or 3 days with question after question on cam shafts, i've read the manuals, websites, and i'm getting there. i understand the basics as far as aggressive cams will leave the valves open longer than stock and longer than mild cams.. also adversely affecting your idle (as far as making it more rough). right now i'm leaning towards some mild cams.. just looking for an even better understanding. a cam 'regrind' by definition is taking material off the cam shaft lobes?

    here as the manual says,
    standard height is 1.7360 inches for intake lobe (with minimum of 1.7281 inches)
    standard height is 1.7560 inches for exhaust lobe (with minimum of 1.7480 inches)
    here is a picture of the afar view of the cam shaft, and to the side is the profile of a lobe



    now what i don't understand, is that if you're 'regrinding' the cam, you're removing height from this lobe... wouldn't this limit the stroke distance and how long each valve is open (lift and duration)? where am i fundamentally going wrong with this guys? i know i'm not a machinist, i just would like a better understanding as far as what a regrind cam is going to provide me? is a regrind replacing the lobes of a camshaft with taller one's.. are the angles just changed on the shaft itself? hopefully someone can point me in the right direction
    peace
    Last edited by Guest; 11-23-2003, 05:28 AM.

    #2
    Yes, somebody please explain this as I don't fully understand it either.
    2013 Dodge Dart Aero

    Comment


      #3
      Re: Cam Shafts

      I don't know if this is what you are looking for but there is more to camshaft specifications than lift. There is also duration, the number of crankshaft degrees the valves remain open (can be different for intake and exhaust). Then there is overlap, the number of crankshaft degrees during which both the intake and exhaust valves are open together (to promote cylinder filling and exhaust gas scavenging at higher rpm's). Finally, there is the rate of acceleration of the cam which determines how quickly the valves reach their maximum lift. In general, the greater the duration and overlap, the "hotter" the cam.
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        #4
        that much i had a full grip on and had pretty much assumed longer duration would leave the cam to get a bit more hotter. what i don't understand is what a regrind is? i could understand by using a 'wider' lobe and/or changing the angles on which the intake and exhaust lobes sit in relationship to each other could have some impact on power, as well as using taller lobes to accomplish a greater degree of each valve's duration and overlap. just by assuming that a cam regrind is removing material from the lobes, it doesn't compute.. i would assume it would perform WORSE than a stock cam. that is what i don't understand.
        peace

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          #5
          When shops regrind cams, they first weld new metal to the cam lobes. Then they re-grind the shape to your specs. they don't just grind the cam as is.

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            #6
            ok, now this means alot more.. now changing the nature of my questioning, if i'm running some cams over to a machinist to get him for a regrind, what specifications should i pass off to him as far as lobe height and what not? (any other specs besides lobe height?) i'm only looking for mild cams as i am not looking to have to get stiffer springs or lock lifters. and for other's reference, what kind of specs would yield a more 'aggresive' cam? thanks
            peace

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              #7
              hey...are there any safety issues that occur with the reground cams? like of things breaking etc?

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                #8
                OK, this is to clarify a few things.

                When you regrind the cam you basically reduce the base circle to achieve the required lift and duration specs. The pointier the cam nose the less duration, more the nose of the lobe is rounder more the cam has duration overall.

                The base circle is the diameter where the valve hasn't moved yet(zero lift) for most Mazda's it's about 1.375" to 1.415" depending on engine model. For the BP engine I beleive it's 1.415". When I regrind your cams I don't add or weld material to the original cam lobes (this is very expensive about $30US/lobe and this is required when you're going after a high lift and high duration value or when valvetrain geometry might get affected) since it's not required for the profiles I offer.

                Basically the new base circle gets reduce to about 1.365" so the new lift is (new height of lobe - base circle = 0.355"). The height of the original lobe was 1.750"and the new height of the regrinded cam lobe is now 1.720". The hydraulic lifter will compensate for the new base circle by getting pumped even more to reach the new base circle. In our example the HLA will compensate for 0.025"((1.415-1.365)/2).

                All the number I used is for explanation purpase only.

                Original cam lobe (base circle 1.415", lobe height 1.750", therefore lift is 1.750-1.415= 0.335")
                Regrinded cam lobe (base circle 1.365", lobe height 1.720", therefore lift is 1.720-1.365 = 0.355")

                THAT'S ALL FOLKS!!!
                92 323 with BP DOHC
                ported/polished head, regrinded cams, JUN adjustable cam gears, ported AFM, ported/knife edged intake manifold.

                N/A project dropped.

                Comment


                  #9
                  well but that affects not only the duration..lift too..or not ?

                  Comment


                    #10
                    it affects both lift and duration.. they are interdependent.

                    addition: like mike said, the hydraulic lash adjusters (HLA's) are fully capable of compensating for cam lobe material loss.. ie a reground cam
                    Last edited by Guest; 11-25-2003, 09:35 PM.

                    Comment


                      #11
                      well.. i got through pricing ALOT of different options, went to a lot of different shops pricing costs, and it breaks down to this.. the cost for ME to throw cam regrinds in on my motor:
                      $250 for Regrinded camshafts with 8.5mm of lift (Mike323's cams.. possibly the best deal.. HKS is next step up around $300 a piece for each cam shaft and offers 8.7mm of lift)
                      $167 for HKS 1.6 miata adjustable cam gears
                      $375 for camshaft installation
                      $20 for new valve cover gasket
                      $225 for 3-4 dyno pulls with air & fuel ratings (1 base run and 3 tunning runs)
                      $85 labor for the dyno tuning
                      ??? for miscellaneous tax and shipping charges

                      i fully calculate my expenses to be well with in the $800 to $1000 dollar range for installation, labor, and materials. overall, gains are questionable (as in no one could honestly sit there and give you an exact figure as to howmuch horsepower gain you would recieve) and a MAJOR limiting factor is the fact that i'm running a stock ecu.. standalone would yield best results. now all of this is granted that i'm not doing an ounce of work, but just so you guys know what you MAY get into, camshafts yield great gains, but have some added costs if you don't install them yourself.
                      peace

                      Comment


                        #12
                        Originally posted by demoninvictus
                        well.. i got through pricing ALOT of different options, went to a lot of different shops pricing costs, and it breaks down to this.. the cost for ME to throw cam regrinds in on my motor:
                        $250 for Regrinded camshafts with 8.5mm of lift (Mike323's cams.. possibly the best deal.. HKS is next step up around $300 a piece for each cam shaft and offers 8.7mm of lift)
                        $167 for HKS 1.6 miata adjustable cam gears
                        $375 for camshaft installation
                        $20 for new valve cover gasket
                        $225 for 3-4 dyno pulls with air & fuel ratings (1 base run and 3 tunning runs)
                        $85 labor for the dyno tuning
                        ??? for miscellaneous tax and shipping charges

                        i fully calculate my expenses to be well with in the $800 to $1000 dollar range for installation, labor, and materials. overall, gains are questionable (as in no one could honestly sit there and give you an exact figure as to howmuch horsepower gain you would recieve) and a MAJOR limiting factor is the fact that i'm running a stock ecu.. standalone would yield best results. now all of this is granted that i'm not doing an ounce of work, but just so you guys know what you MAY get into, camshafts yield great gains, but have some added costs if you don't install them yourself.
                        peace
                        You can do much better than that.
                        I can get adjustable OBX cam gear for $140 for the pair. Also the cam installation is about 4 hours of labor, your garage is charging you an arm and a leg, it 30 minutes more on top of changing the timming belt. As for the dyno run I suggest you look elsewhere, I can get it for about $80/hour. All you need is the most 1.5 hour to perform 10-12 dyno runs. Perform the following runs:

                        1) 0 I, 0 E
                        2)+3 I, 0 E
                        3)+3 I, +3 E
                        4) +3 I, -3 E
                        5) - 3 I, 0 E

                        + = advance
                        - = retard
                        I = intake cam
                        E = exhaust cam

                        Once you've performed all the 5 runs this will give you a good indication which whay you want to go next. Let say you get great results with runs 2 and 3 than you perform another run with +3I, +2 E and another at +5I, +2E and so on, if you don't see much of a difference than leave thing as they where prior to this change.

                        You don't need an ECU since we don't add extermly aggressice cams, a reprogrammed ECU will help but not by allot.
                        92 323 with BP DOHC
                        ported/polished head, regrinded cams, JUN adjustable cam gears, ported AFM, ported/knife edged intake manifold.

                        N/A project dropped.

                        Comment


                          #13
                          When you do dyno pulls are you the one driving your car, or does someone from the shop do the driving?
                          2013 Dodge Dart Aero

                          Comment


                            #14
                            Originally posted by Marc93lx
                            When you do dyno pulls are you the one driving your car, or does someone from the shop do the driving?
                            How is this question relevant. It doesn't make a difference who takes the car to 4th gear up to 7200rpms on the rollers.
                            92 323 with BP DOHC
                            ported/polished head, regrinded cams, JUN adjustable cam gears, ported AFM, ported/knife edged intake manifold.

                            N/A project dropped.

                            Comment


                              #15
                              well.. there are not a lot of shops around here that do 'Internal' engine work as they say... and not alot of shops that are experienced in mazda's .. maybe a few dsm's, and a ton of honda's, but are seemingly afraid of the bp.. for no reason i would assume just the fact that not alot of protege guys around here do that kind of work to their engines. one shop wanted to charge me 6 - 8 hours of labor, one said it would be a whole day, one said 5 hours of labor.. and at that.. it was 375 going rate. i still have to look at a few other shops to see if i can get this kind of work done, however as far as dyno's.. thats the going rate. there are NO other shops that do dyno's around here for the public. trust me, after phone tagging around, i've found one shop fully capable of doing everything that i needed. if you know any mechs that do this kinda work in the tri-state area (pa, nj, de.. or even md) let me know. i still haven't given up on the idea, though cost is a big factor, i will definately have to look around more than i have.
                              peace

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